linux-kernel - Re: [PATCH v3 12/14] fs/configfs: Add a callback to determine attribute visibility

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Date: Mon, 15 Apr 2024 22:46:08 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Tom Lendacky <thomas.lendacky@....com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, <linux-coco@...ts.linux.dev>, <svsm-devel@...onut-svsm.dev>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, "Peter
 Zijlstra" <peterz@...radead.org>, Dan Williams <dan.j.williams@...el.com>,
	Michael Roth <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>,
	Joel Becker <jlbec@...lplan.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 12/14] fs/configfs: Add a callback to determine
 attribute visibility

Tom Lendacky wrote:
> In order to support dynamic decisions as to whether an attribute should be
> created, add a callback that returns a bool to indicate whether the
> attribute should be display. If no callback is registered, the attribute

s/display/displayed/

> is displayed by default.
> 
> Cc: Joel Becker <jlbec@...lplan.org>
> Cc: Christoph Hellwig <hch@....de>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  fs/configfs/file.c       |   7 +++
>  include/linux/configfs.h | 111 +++++++++++++++++++++++++++------------
>  2 files changed, 84 insertions(+), 34 deletions(-)
> 
> diff --git a/fs/configfs/file.c b/fs/configfs/file.c
> index 0ad32150611e..a976c183756c 100644
> --- a/fs/configfs/file.c
> +++ b/fs/configfs/file.c
> @@ -451,6 +451,9 @@ int configfs_create_file(struct config_item * item, const struct configfs_attrib
>  	umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
>  	int error = 0;
>  
> +	if (attr->is_visible && !attr->is_visible(item, attr))
> +		return 0;
> +
>  	inode_lock_nested(d_inode(dir), I_MUTEX_NORMAL);
>  	error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode,
>  				     CONFIGFS_ITEM_ATTR, parent_sd->s_frag);
> @@ -470,9 +473,13 @@ int configfs_create_bin_file(struct config_item *item,
>  {
>  	struct dentry *dir = item->ci_dentry;
>  	struct configfs_dirent *parent_sd = dir->d_fsdata;
> +	const struct configfs_attribute *attr = &bin_attr->cb_attr;
>  	umode_t mode = (bin_attr->cb_attr.ca_mode & S_IALLUGO) | S_IFREG;
>  	int error = 0;
>  
> +	if (attr->is_visible && !attr->is_visible(item, attr))
> +		return 0;
> +
>  	inode_lock_nested(dir->d_inode, I_MUTEX_NORMAL);
>  	error = configfs_make_dirent(parent_sd, NULL, (void *) bin_attr, mode,
>  				     CONFIGFS_ITEM_BIN_ATTR, parent_sd->s_frag);
> diff --git a/include/linux/configfs.h b/include/linux/configfs.h
> index 2606711adb18..c836d7bc7c9e 100644
> --- a/include/linux/configfs.h
> +++ b/include/linux/configfs.h
> @@ -116,35 +116,57 @@ struct configfs_attribute {
>  	const char		*ca_name;
>  	struct module 		*ca_owner;
>  	umode_t			ca_mode;
> +	bool (*is_visible)(const struct config_item *, const struct configfs_attribute *);
>  	ssize_t (*show)(struct config_item *, char *);
>  	ssize_t (*store)(struct config_item *, const char *, size_t);
>  };
>  
> -#define CONFIGFS_ATTR(_pfx, _name)			\
> +#define __CONFIGFS_ATTR(_pfx, _name, _vis)		\
>  static struct configfs_attribute _pfx##attr_##_name = {	\
>  	.ca_name	= __stringify(_name),		\
>  	.ca_mode	= S_IRUGO | S_IWUSR,		\
>  	.ca_owner	= THIS_MODULE,			\
> +	.is_visible	= _vis,				\
>  	.show		= _pfx##_name##_show,		\
>  	.store		= _pfx##_name##_store,		\

Shouldn't this operation live in configfs_group_operations? That would
mirror the sysfs organization, and likely saves some memory.